The everting catheter has been shown to be a reliable clinical means to catheterize long, small diameter, and highly tortuous blood vessels, inaccessible by previous techniques. An everting element evaginates from the tip of a conventional catheter. This extremely flexible polyurethane element has been fabricated in 3, 4 and 5 French sizes mated with 5, 6 and 7 French catheters, respectively, and is capable of eversion lengths in excess of 40 cm. The catheter has been applied clinically for the local delivery of chemotherapy to brain tumors and of embolizing agents in the liver. In the former, treatment is provided by positioning the conventional catheter in the internal carotid artery from a femoral entry; everting the element through the carotid sinus, beyond the ophthalmic artery to avert retinal toxicity; and perfusing the tumor through the middle and/or anterior cerebral arteries. Note that a conventional catheter cannot safely negotiate the tortuosity of the carotid sinus. In the latter application, embolizing agents are delivered intra-arterially to block the perfusion of hepatic tumors. The sinuousity of the vessel precludes access by conventional techniques. In catheter has been extensively used clinically in its present prototype form, and production techniques for its fabrication have been transferred to private industry to provide for a ready source of catheters for future studies.